Method of determining the content of foreign substances in iron and steel



June 25, 1929. B ENLUND- 1,718,687

IfiETHOD OF DETERMINING THE CONTENT OF FOREIGN SUBSTANCES IN IRON ANDSTEEL Filed Aug. 16, 1927 SPEC. ausc. RESISTANCE lo HARDENED MATERIALsPsc. mac.

\ RESISTANCE ANNEALED MATERIAL %cmuaor K 45 x7 m INVENTOR alaon DAVIDENLUND.

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f atentetl dune application-filed august ltd, 1192'? serial Itto.2135296.

The primary object of my invention is to provide a method fordetermining the content of a foreign substance in iron and steel bymeasuring the specific electric resistance of the same and applying themeasurement to a chart on Which the result "can be directly de terminedvvithout calculations.

llnother object is to provide such a method vvhich is readily adaptablefor use both at the furnaces or point of manufacture as Well as in thelaboratories and places of use. By my improved method, the percentagecontent of foreign substances of iron and steel may be determinedreadily and quickly Without the necessity of mathematical calculations,thus making it possible to rapidly test the material for thesepercentages and to do so with relatively unskilled labor.

My improved method is based upon the measurement of the specificelectric resistance in iron and steel in a given state of hard ened andannealed or normalized or other-- Wise vvorlred conditions. Through thevalue of this specific electric resistance, ll can ob tain thepercentage content of foreign substances in the material. f accomplishthis purpose by the use of suitable charts which l have prepared andWhich are used in conjunction with a suitable instrument for rneasur ingthe specific electrieresistance of the material, llhesc charts have beenprepared With vievv to eliminate all necessity of calculations in orderthat accurate readings may be made by an unskilled party or one notfamiliar with the "mathematical calculations necessary to determiningthe content of for eign elements in a given material.

Referring now to the figures of the drawing wherein like referencenumerals indicate litre parts Figure l is a diagrammatic viewillustrating a form of apparatus for measuring the specific electricresistance of the material t be tested.

Figure 2 is a plan view of a chart used in connection with theresistance measuring apparatus upon which can be read the carbon contentof the tested material.

It should he stated at the outset that if in iron or steel a foreignsubstance or foreign substances are included in varying percentages, thespecific electric resistance of the material will necessarily vary withthe percentages of such foreign substance or substances. Obviously,therefore, if these foreign sub-' stances give to the material differentproperties when such substances are present in greater or lesspercentages, it is obvious that those changes in properties of thematerial are in a more or less degree directly in rela tion to thepercentages of such foreign substances and accordingly can be measuredby the varying specific electric resistance of the material.

lln describing my invention, ll Will use as an illustration of theapplicability thereof, the method of determining the percent of carbonin steel,

I "Will now describe my invention in connection With the determinationof the percent of carbon in steel, this being illustrative of the Wideapplication of' my invention,

lfn carrying out my method for determining the carbon content in steel,a length of steel is taken of a suitable cross section, limitedonly bythe size of the apparatus used for making the measurements. ff thetesting method is tobe performed at the furnaces, this length of testbar may be di rectly rolled or forged to the required sine, lit themeasurement is to be made in the laboratory, it may be taken fromstoclr. From one end of this test bar, there is measured. off a givenlength of say one foot. it. marlr,

preferably a chisel cut is made at this point in the bar, and the end somarked off is then heated in any desired manner to say l,tl00 de grcescentigrade. This heated end is there upon quenched in Water or oil, orotherwise rapidly cooled and broken from the bar at thechisel cut ormark. There is thus pro-- vided a test bar of hardened steel. it similarlength is now measured ofl' upon the remain-- thii ing bar and similarlymarked or cut and like Wise heated to the same temperature. This portioninstead of being rapidly cooled, is

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' allowed to cool slowly and when cooled is broken off at the mark orcut. This provides a second test bar of annealed or normalized steel,one being hardened and the other annealed, or normalized. With thesetest bars,

, the measurements are made for this specific in the clamps 1, and thecontacts 2 engaging the ends thereof, the switch 5 is closed allow-. mgthe current from the battery 4 to pass through the test bar and registerupon the volt meter and ampere meter, readings from which the specificelectric resistance of the test bar in micro-ohms can be, readilycomputed. This resistance is noted and the hardened test bar'removedfrom the measuring apparatus and the annealed or normalized test barplaced therein and its specific electric measuring its resistance.

It should be stated here that the particular resistance likewisemeasured and this specific res stance noted. In Figure 1, the referencecharacter 8 indicates a test bar in position for apparatus for measuringthe specific electric resistance of these test bars, forms no part ofthe. inventioaherein described and claimed, and many forms of apparatusmay be substituted for that shown. In fact, any suitable electricresistance .mea'suringapparatus may be employed in carrying out myinvention.

Now having the specific electric resistance of the hardened test bar andof the annealed, or normalized test bar, it is desired to determine thepercent of carbon in the steel from which these test bars are taken. Forthis purpose, a chart such as that shown in Figure 2 is used. It'will benoted that on this chart,

there is a scale at the left indicated at 9 graduated in units ofresistance, preferably micro-ohms and reading from top to bottom. Onthe'right of the chart, there is a similar though shorter scalecalibrated in thesame units of resistance'and on the same proport1onwith the scale on the left, this scale, however, reading from bottom to,top. This scale 1s indicated at 10. Assuming now that the specificelectric resistance of the above mentioned hardened test bar measured 25microohms and the specific electric resistance of the annealed ornormalized test bar measured 15 micro-ohms, the tester now takes astraight edge such as a transparent rule 11, placing one edge thereof atthe point 25 on the left hand scale and the same edge at the point 15 onthe right hand scale. The point at which this straight edge 11 crossesthe middle scale 12, calibrated in units of percentage, indicates t0 theoperator at a glance the percent of carbon in the steel which has beentested.

This chart may be made up by performing a series of tests, that is,mcasuren'ients of specific electric resistance, of test pieces ofsteelhavingknown percentages of carbon, and

' the scales arranged on the chart in such mannor that in comparing thespecific electric resistance measurements as above described, the middlescale will properly indicate the carbon percent.

It will be understood that other types and forms of charts than thatherein shown may be prepared to accomplish the same purpose. The oneillustrated, however, is illustrative of a Very sim )le form, by meansof which the percentage of foreign substances in the material to betested can be quickly and accurately determined once the specificelectric resistance of the material is measured.

By this method the makers of steel can quickly and easily gaugeaccurately the quality of the product. Likewise, the purchaser or userof steels can similarly and very quickly check up by the same methodTand determine if the delivered material is according to thespecifications as ordered.

Obviously, many changes may be made by way of detail in the form' andmethod of use of my invention without departing from the spirit andscope thereof. I do not limit myself therefore to "the forms shown anddescribed herein other than by the appended claims.

I claim 1. The method of determining the percentage of a foreignsubstance in iron and steel, including the steps of measurin thespecific electric resistance of hardene and annealed or normalized testpieces of the material to be tested and comparing such measurements withknown factors.

2. The method of determining the percentage of a foreign substance iniron and steel, including the steps of measnrin the specific electricresistance of hardened and annealed or normalized test pieces of thematerial, and comparing such measurements with indications ona preparedchart from which can be read directly the percentage of such foreignsubstance for said measurements.

3. The method of determining the percentage of a foreign substance iniron and steel, including the steps of measuring the specific electricresistance of hardened and annealed or normalized test pieces of thematerial, comparing such measurements on independent scales of a chartand rcadinr diwinner ll centage of carbon content in iron and steelincluding the steps of making two test hars from such material, onehardened and the other annealed 0r normalized, measuring the specificelectric resistance of said test bars,

comparing said measurements on oppositely disposed scale of a chart,placing a straight edge across said scales at the point of suchmeasurements and reading directly from a third scale between said firsttwo mentioned 10 scales, the percentage of the carbon content at thepoint Where said straight edge crosses said central scale.

lBRUR DAVlD ENLUND.

